Integrated circuits (ICs) and other electronic devices often include arrangements of interconnected field effect transistors (FETs), also called metal-oxide-semiconductor field effect transistors (MOSFETs), or simply MOS transistors or devices. A typical MOS transistor includes a gate electrode as a control electrode, and spaced apart source and drain electrodes. A control voltage applied to the gate electrode controls the flow of current through a controllable conductive channel between the source and drain electrodes.
Power transistor devices are designed to be tolerant of the high currents and voltages that are present in power applications such as motion control, air bag deployment, and automotive fuel injector drivers. One type of power MOS transistor is a laterally diffused metal-oxide-semiconductor (LDMOS) transistor. In an LDMOS device, a drift space is provided between the channel region and the drain region.
LDMOS devices are often used in applications, such as automotive applications, involving operational voltages greater than 40 volts. Various features of the LDMOS devices are designed to increase the voltage at which device breakdown (e.g., avalanche breakdown) occurs. For example, breakdown is often prevented through a reduced surface field (RESURF) structure in the LDMOS device design. The RESURF structure is designed to deplete the drift space of the LDMOS device in both vertical and lateral directions, thereby reducing the electric field either near the edge of, or inside, the drift region and thus raising the off-state breakdown voltage (BVdss) of the device. Unfortunately, RESURF structures only address breakdown in areas near or inside the drift region. The breakdown voltage of the device may be established by breakdown that occurs in other locations.